title: Identification of QTLs conferring resistance to downy mildew in legacy cultivars of lettuce.
abstract: Many cultivars of lettuce (Lactuca sativa L.), the most popular leafy vegetable, are susceptible to downy mildew disease caused by Bremia lactucae. Cultivars Iceberg and Grand Rapids that were released in the 18th and 19th centuries, respectively, have high levels of quantitative resistance to downy mildew. We developed a population of recombinant inbred lines (RILs) originating from a cross between these two legacy cultivars, constructed a linkage map, and identified two QTLs for resistance on linkage groups 2 (qDM2.1) and 5 (qDM5.1) that determined resistance under field conditions in California and the Netherlands. The same QTLs determined delayed sporulation at the seedling stage in laboratory experiments. Alleles conferring elevated resistance at both QTLs originate from cultivar Iceberg. An additional QTL on linkage group 9 (qDM9.1) was detected through simultaneous analysis of all experiments with mixed-model approach. Alleles for elevated resistance at this locus originate from cultivar Grand Rapids.
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, U.S. Agricultural Research Station, 1636 E. Alisal St, Salinas, CA 93905, USA.
authors.forename: Ivan
authors.initials: I
authors.lastname: Simko
authors.forename: Amy J
authors.initials: AJ
authors.lastname: Atallah
authors.forename: Oswaldo E
authors.initials: OE
authors.lastname: Ochoa
authors.forename: Rudie
authors.initials: R
authors.lastname: Antonise
authors.forename: Carlos H
authors.initials: CH
authors.lastname: Galeano
authors.forename: Maria Jose
authors.initials: MJ
authors.lastname: Truco
authors.forename: Richard W
authors.initials: RW
authors.lastname: Michelmore
mesh_terms: D000483:Alleles; D002874:Chromosome Mapping; D060467:Disease Resistance / Q000235:genetics* / Q000276:immunology; D008040:Genetic Linkage; D005838:Genotype; D018545:Lactuca / Q000235:genetics* / Q000276:immunology / Q000382:microbiology*; D009868:Oomycetes; D010935:Plant Diseases / Q000235:genetics* / Q000276:immunology; D040641:Quantitative Trait Loci